// the loop routine runs over and over again forever:
void loop() {
digitalWrite(led3, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100); // wait for a second
digitalWrite(led2, LOW); // turn the LED off by making the voltage LOW
delay(100); // wait for a second
digitalWrite(led4, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100); // wait for a second
digitalWrite(led3, LOW); // turn the LED off by making the voltage LOW
delay(100); // wait for a second
digitalWrite(led5, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100); // wait for a second
digitalWrite(led4, LOW); // turn the LED off by making the voltage LOW
delay(100); // wait for a second
digitalWrite(led6, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100); // wait for a second
digitalWrite(led5, LOW); // turn the LED off by making the voltage LOW
delay(100); // wait for a second
digitalWrite(led6, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100);

digitalWrite(led5, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100);
digitalWrite(led6, LOW); // turn the LED off by making the voltage LOW
delay(100);
digitalWrite(led4, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100);
digitalWrite(led5, LOW); // turn the LED off by making the voltage LOW
delay(100);
digitalWrite(led3, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100);
digitalWrite(led4, LOW); // turn the LED off by making the voltage LOW
delay(100);
digitalWrite(led2, HIGH); // turn the LED on (HIGH is the voltage level)
delay(100);
digitalWrite(led3, LOW); // turn the LED off by making the voltage LOW
delay(100);
digitalWrite(led2, LOW); // turn the LED off by making the voltage LOW
delay(100);

}

This gives us a electronic pendulum who’s delay time can be controlled as according to our wish.